Fuel injected internal combustion engines are well known. Fuel injection arrangements may be divided generally into multi-port fuel injection (MPFI), wherein fuel is injected into a runner of an air intake manifold ahead of a cylinder intake valve, and gasoline direct injection (GDI), wherein fuel is injected directly into the combustion chamber of an engine cylinder, typically during or at the end of the compression stroke of the piston. GDI is designed to allow greater control and precision of the fuel charge to the combustion chamber, resulting in better fuel economy and lower emissions. This is accomplished by the combustion of a precisely controlled mixture under various operating conditions. GDI is also designed to allow higher cylinder compression ratios, delivering higher performance with lower fuel consumption compared to other fuel injection systems.
Generally, an electromagnetic fuel injector incorporates a solenoid armature, located between the pole piece of the solenoid and a fixed valve seat. Electromagnetic fuel injectors are linear devices that meter fuel per electric pulse at a rate proportional to the width of the electric pulse. The armature typically operates as a movable valve assembly. In a normally-closed injector, when the injector is de-energized, its movable valve assembly is released from one stop position and accelerated by a spring towards the opposite stop position, located at the valve seat. The distance between the stop positions constitutes the stroke.
A solenoid actuated fuel injector for automotive engines is required to operate with a small and precise stroke of its core or valve in order to provide a fuel flow rate within an established tolerance. The stroke of the moving mass of the fuel injector is critical to function, performance, and durability of the injector. Moreover, since GDI Injectors require a relatively high fuel pressure to operate that may be, for example, as high as 1700 psi compared to about 60 psi required to operate a typical MPFI injector, the fuel flow of GDI injectors is more sensitive to variations in stroke than MPFI injectors. Thus, a tighter control of the stroke set, such as about ±5 microns, is needed in GDI injectors.
In some current injectors, the stroke is adjusted at assembly by moving an adjustable valve seat a predetermined dimension from a seated valve position after related components are first crimped or welded in place. This allows the stroke setting operation to compensate for assembly tolerances which result from the crimping or welding operations. However, the requirement for an adjustable valve seat adds cost and complexity to the assembly process.
Other prior art stroke adjusting methods for solenoid operated injectors include, for example, pre-measurement of stroke followed by shimming to obtain a desired target stroke, movement of a component followed by welding or staking of that component to set the stroke, or application of multiple axial laser weld stitches to set the stroke. Setting the stroke in some of these ways typically leads to a change in the setting caused by the welding or staking, thereby increasing the tolerance capability of the process. Moreover, these stroke setting methods described do not readily allow for a static flow setting process.
What is needed in the art is a stroke setting method for a solenoid actuated fuel injector that permits an accurate adjustment of the static flow and that does not require welding or mechanical deformation processes to be performed after the stroke adjustment is made.
It is a principal object of the present invention to provide a method for externally setting the stroke and the static flow of the injector while in cartridge form as well as in final assembly form.